Importance of vegetation structure and floristic composition in lark sparrow habitat use

Background/Question/Methods Woody invasion due to fire suppression alters the vegetation structure and floristic composition of early-successional plant communities. Studies have indicated that both vegetation structure and floristic composition are important in grassland birds’ habitat requirements, though the relative importance of each has been debated. In Northwest Ohio’s Oak Openings Region, a state endangered bird, the Lark Sparrow, relies on an early-successional plant community for nesting habitat. The plant community, globally rare Midwest sand barren, has been heavily impacted by fire suppression. Managers use prescribed burns and mowing to maintain some Midwest sand barrens in an early successional state. The objective of our study was to determine Lark Sparrows’ breeding habitat requirements in this impacted and managed landscape by looking at multiple spatial scales: pairs’ breeding territories, sand barren habitat patches, and the landscape. Our methods included on-the-ground measurements of vegetation structure and floristic composition and GIS analysis of landscape characteristics for two categories of sites: sites currently used by Lark Sparrows and sites previously used but abandoned by Lark Sparrows. By analyzing which habitat components were significantly different between these presence and absence sites, we created a predictive model of Lark Sparrow breeding habitat that compares the importance of vegetation structure, floristic composition, and landscape characteristics.

Results/Conclusions Our results indicate that low vegetation density, ~8% shrub cover, ~9% tree cover, sandy soil, and barrens larger than 1.9 ha are important predictors of Lark Sparrow presence. Preliminary results of floristic composition analysis suggest that bare sand and clump grasses are important. At large spatial scales (landscape) habitat patch size, soil, and elevation are important predictors of Lark Sparrow habitat use. At intermediate spatial scales (i.e. barrens) vegetation structure is important, but at smaller scales (i.e. a pair’s breeding territory) floristic composition is important. These results suggest that birds dependent on early successional habitats may use vegetation structure to locate potentially suitable habitat, but the birds’ success may depend on local scale factors such as floristic composition. This message is important for managers restoring early successional plant communities: altering vegetation structure by removing woody invaders with fire or mowing is crucial, but floristic composition and other local scale habitat components should be monitored.